Flotation reagent



FLOTATION REAGENT Edmund A. Schoeld, John M. Fritschy, and Jack D.

Nabors, Carlsbad, N. Mex., assignors to Potash Company of America, Carlsbad, N. Mex., a corporation of Colorado Filed May 23, 1956, Ser. No. 586,649

No Drawing.

3 Claims.

This invention relates to the beneficiation of mineral values from their ores, and more particularly to the concentration of coarse, granular potash minerals by preferential, frothless flotation and to reagent combinations for producing the preferential flotation.

or other wet separations. In the potash industry, and particularly the potash ore as mined in the Carlsbad, New Mexico, district, froth flotation has been extensively used to concentrate the potash alues. The potash ore (sylvinite) obtained from the Carlsbad area may, in general, contain about 40% potassium chloride (sylvite) and about 60% sodium chloride (halite) with minor impurities such 7 as water insoluble materials, magnesium and calcium, sulfates, and like compositions. 'As practised in the potash industry, froth flotation benefication has been highly developed, and it is a process in which the ore is reduced to a relatively fine size, generally less than about 14 mesh, and most commonly below about 28 mesh. Tyler mesh screen sizes are used throughout the specification in referring to the size of particles.

While the major portion of the potash produced in this country is ultimately used in the agricultural industry .Where the size of product has no particular significance, the larger granular potash sizes have, generally, been found to be most desirable for agricultural use. In the larger sizes, the potash concentrates cake less readily than the smaller sizes, and thus they are easier to handle to uniformly spread in fertilizing. Also, from the concentrating consideration, the larger particle sizes are more desirable since the grinding costs of the ore are substantially reduced.

The maximum size of the ore particles that may be beneficiated is, however, limited by the nature of the reagents used in the beneficiation, the flotation equipment and the actual physical constituents of the individual ore particles being processed. The particles of the sodium chloride and potassium chloride must be physically separated in order that beneficiation of one or the other of the ingredients may be performed. A coarse potash ore fraction, normally, will contain a considerable amount of potassium chloride which is not physically liberated from the sodium chloride; in other words, individual particles 'will contain portions of sodium chloride and potassium chloride cemented together. The particles which contain both of the major ingredients of the ore are called middlings. In a beneficiation process, a portion of the middlings will react in the process much the same as the potassium chloride crystals and will, in certain instances,

'float with the potassium chloride decreasing the grade of the beneficiated concentrate to such an extent that the concentrate is so contaminated with sodium chloride as to be substantially unmarketable. In order to produce a .plus 28 mesh range.

than the desired .size range.

2,935,751 Patented May 24, 1960 ice potassium chloride product of about potassium chlo ride, as is now a commonly accepted standard product in the industry, the maximum size. of the ore particles is limited to about a 6 or an 8 mesh size. This limit prevents the inclusion of an excess of middlings in the concentrate, but even at this size enough middlings are present that special techniques must be used to obtain a satisfactory product.

In our co-pending application, Serial No. 526,720, filed August 5, 1955, now abandoned, Beneficiation of Potash Ores, there is described a new type of equipment for a flotation of coarse potash ores, and in co-pending application, Serial vNo. 514,752, filed June .10, .1955, now abandoned, Combined Flotation Reagent, there is described a novel reagent which is effective in the technique of float- .ing the coarse ore. in referring to coarse ore it is intended to mean that the particle size distribution of the crushed ore is larger than is usually considered amenable to froth flotation using commonly known flotation equipment and reagents. The size of the ore particles handled in the tests, detailed below, was generally in the minus 6 to plus 20 mesh range, although the actual size of the ore on a commercial basis would obviously depend upon the characteristics of the particular ore. Such characteristics would include the average particle size of the finite crystals in the natural ore, and the extent to which the crushed product consists of relatively pure crystals or of middlings. If there is an excess of middlings in this size range, further crushing of the middlings is necessary for separation of the majorconsitutuents of the middlings.

According to the present invention, we have discovered new reagents which are effective in securing a very rapid, frothless flotation of coarse particles of sylvite from a sylvinite ore. The equipment as described in our copending application Serial No. 526,720 is effective in utilizing the new reagents, and improved equipment described in co-pending application, Serial No. 595,500, filed July 2, 1956, for Method and Apparatus for Flotation Concentration in-Coarse Size Range, also, provides efiective and eflicient equipment for producing a high-grade, coarse potash product by the flotation. In our earlier application, Serial No. 514,752, the mixed reagent utilized an aliphatic amine as the fundamental activator and hydroabietyl alcohol as the collector for the coarse sylvite. Kerosene was utilized as a typical solvent for the mixture; This .mixture works effectively when applied to an ore which has been suspended in a brine and then drained relatively free of the brine. We have now found that the amine and the modifier or collector may be applied separately and in various forms to produce new and effective flotation reagents. In using the present invention no solvent is generally required but some liquids which maybe used actually exert additional collecting action on the sylvite.

In utilizing the invention of the present application for the beneficiation of potash ores, the ore as mined is first crushed to provide a product'in the minus 6 to The crushed ore is then screened to remove the fine ore particles and also the ore coarser The ore of the desired size fraction is then slurried with a brine of the soluble constituents of the ore and then drained to removeslime, fine particles, and brine solution therefrom; Normally the brine is saturated with respect to one of the soluble ingredients of the ore, generally the potassium composition. A reagent according to the invention may then be added to the wet, drained ore, and the ore is thoroughly mixed or conditioned so as to disperse the reagent into the ore. The conditioned .ore is then 'subjected to treatment in a flotation cell.

The reagent, which consists of an amine, which ffirst preferentially coats the potash material, and a modifier, is added to the drained ore so as to effectively float the sylvite particles from the halite in the ore. In conditioning the ore for the coarse ore flotation, the amine may be applied separately or in combination with the modifier. When added separately, the amine may be added as a solution or an emulsion and the modifying agent is simultaneously added in another stream. Under certain conditions, it may be desirable to introduce the amine into the drained ore, condition the ore with the amine and then subsequently add the modifying reagent with further conditioning for the modifying agent.

The aliphatic amines which may be used in the process are straight-chain alkylamines which are known to be useful as collectors for sylvite, and they may extend from octyl to octadecyl or even longer chain lengths. The hydrocarbon chain is derived, generally, from animal fats which contain a certain proportion of unsaturated chains such as oleic acid. Amines prepared from beef tallow have been most widely used in the froth flotation field. By hydrogenation, the unsaturated hydrocarbon chains may be converted to saturated chains in the amine reagent. The extent of saturation determines the melting point and the solubility of the amines. The amount of hydrogenation is, of course, determined by the desired characteristics The amines may be used individually or as combinations of various amines, and the mixtures of the amines need not necessarily consist of all saturated or all unsaturated chains, but may, obviously, be a mixture to obtain the desired melting point or solubility. The amines are normally used as salts since the salts have a greater solubility than the amines themselves. The most commonly used amine salt is the acetate, but the hydrochloride and like salts have also been used. Such amines as are normally used in the flotation field may contain traces of secondary and tertiary amines and/or salts thereof.

While both saturated and unsaturated aliphatic amines are useful in the process, the hydrogenated or saturated aliphatic amines are superior to unsaturated compounds for a coarse oreflotation according to the invention, and, therefore, the hydrogenated or saturated aliphatic amines are the preferred amines. These saturated aliphatic amines are relatively insoluble in water, and have not had very extensive use in the potash industry. By making an emulsion of such an amine in water to produce about a three percent by weight suspension, at very stable mixture may be formed. The emulsions may best be prepared from the aliphatic amines by heating to melt the same, and then pouring the melted amine into water containing enough acid to neutralize a portion of the amine. In one preferred form, using a three percent solution, suflicient acid to neutralize about thirty percent of the amine produces an emulsion of medium-heavy consistency, but this may be varied over very wide limits by varying the amounts of acid.

The modifiers which may be used with the aliphatic amines may be one of the class of high molecular weight alcohols, esters of high molecular weight organic acids and amides of high molecular weight fatty acids. A modifier of the rosin type, such as hydroabietyl alcohol, rosin or oxidized turpentine, as prescribed in application Serial No. 514,752, referred to above, provides an effective and eflicient modifier for the amine.

Other alcohols include aliphatic alcohols, particularly the branched type which include such compounds as 2- ethyl-hexyl alcohol, methyl-amyl alcohol, commercial iso-octyl alcohols which are generally dimethyl hexanols, mixtures of isomers rather than pure iso-oetyl alcohols. Such alcohols may be used alone with an amine, but their effectiveness is increased when used in combination with other modifiers of higher molecular weight. Certain cyclic alcohols such as hydroabietyl alcohol, described .above, paramenthane alcohol, pinane alcohol, and the like are, also, effective in the flotation of a coarse potash.

The esters of the high molecular weight organic acids include such compositions as methyl stearate, methyl oleate, glyceryl stearate, various alcohol esters of such acids produced from natural materials which include tallow, fish oils, cottonseed oil or the hydrogenated natural materials, etc. Other esters of acids may be of the abietic acid type. Esters of tall oil, which is a mixture of resin acids and fatty acids are effective modifiers. In a similar manner, methyl ester of abietic acid is an effective modifier.

Naturally occurring fats and oils such as tallow, cottonseed oil, lard, linseed oil, corn oil, olive oil and the like, which are generally glycerol compounds of the fatty acids are very effective as modifiers of the amines in the coarse flotation.

The amides of the high molecular weight fatty acids includes amides prepared from tallow and other natural fatty materials, and in general, the amides are prepared commercially from substantially the same range of raw materials as are the amines. These amides impart an additional hydrophobic character to the amine coating on the sylvite particles.

There are probably two modes of action in which these modifiers act on the amine coating. The iso-octyl alcohols probably fill in spaces between the hydrocarbon ends of the amine molecules and thus make a better coating. The hydroabietyl alcohol probably covers and bridges over spaces between the amine molecules. With the aliphatic alcohols and hydrocarbons relatively smaller molecules are effective; with alieyclic compounds steric hindrance prevents positioning between amine molecules and sorption must be at the surface. With the aromatic compounds similar steric conditions exist. Weakly polar groups probably assist in distribution but may have little value beyond that. As the molecular weight increases it becomes increasingly difficult to distribute the modifier on the amine surface and solvents may, therefore, assist by aiding distribution. If the solvent itself has some activity it can assist in both modes of action.

In closely observing froth flotation of sylvite it is found that at the surface many sylvite particles are distributed on each bubble and the mass of bubbles tend to keep the mass of froth light and floating on the surface of the liquid. In the liquid it is found that one bubble often attaches to several crystals and is able to carry them to the surface.

In the present new concept of frothless flotation the particles may remain on the surface unsupported by a froth and apparently held by the surface tension of the liquid. The liquid is unable to wet the individual particle, and it therefore does not fall through the surface.

Also, in the liquid several bubbles may attach to one sylvite particle and thus carry it to the surface. Intense aeration, without undue particle scrubbing, supplies the numerous bubbles which then complete the action very quickly.

In an action as described in copending application 526,720, as the fluid flows over the weir of the cell it may carry some particles that have risen nearly to the surface but still have not reached the surface. This sweeping over of particles limit the smaller size of particles that can be included as feed for the cell. If a small halite particle reaches near the surface it could be swept over into the concentrate. This, also, makes the upward flow of brine undesirable. The mechanism of the flotation action is one of air bubbles doing the levitation and the flow of brine is kept to the minimum amount that will maintain the mass of solids fluid and carry oif products.

The collector reagent for the present invention builds up a multiple layer on the mineral particles so as to give them a strong hydrophobic property. To obtain this result, the amine is an activator providing a thin coating on the particles to which the modifier can attach. The

modifier, therefore, is actually the flotation collector. The amine reagent is selective and readily attaches itself to the sylvite particle. The modifier is not selective and will not attach to the particle surfaces. The modifier must exert some attraction for the hydrocarbon ends of the amine reagent so that it may hold onto the particle and build up a flotation coating. The combined ingredients produce a reagent which provides a double coat for the particles, which coating is considerably more hydrophobic than the amine by itself. Particles so coated make air contact very easily, and the rising bubbles carry the particles to or near the surface. As the particle reaches the surface of the brine and contacts the atmosphere, the surface tension of the brine supports the product. Particles on the surface and near the surface will be carried over the weir of the cell.

In general, the modifying agents of the invention are weakly polar or non-polar and therefore have but little surface activity in and of themselves and do not function as selective collectors. The modifier attaches to the hydrocarbon or oily ends of the amine molecules which are attached by their hydrophilic ends to the particular 'values of the ore. The hydrophobic modifying materials,

which are elfective in the reagent of the present invention, are those which have a contact angle greater than that of the amine with which it is used. The contact angle is measured by using a captive bubble in water and in contact with a glass plate coated with the modifier reagent and measuring the angle between air-water and water-solid interfaces. For example, an amine shows a contact angle with air and water of 58 degrees, as measured by the captive bubble method. By adding hydroabietyl alcohol to the amine coating, however, the contact angle is increased to 106 degrees, which means that the coating has a much greater alfinity for air. The particles so coated with the combination reagent float very easily and are literally ejected from the brine medium. The modifiers of the invention will not react with the amine nor with the brine,'and are not adsorbed directly on the mineral surfaces. These modifiers do have an aflinity for an adsorbed amine film and on being adsorbed by the amine film will form a layer which is more hydrophobic than the amine layer alone.

The tests which were conducted on the various reagent materials are summarized below giving the amine rate used, the modifier rate and the grade of the tails produced. In the tests, an ore of about forty percent sylvite was used in all instances, but a variance in the grade of the feed does not substantially change the result. Also, in the tests, reagent rates were used which would give a comparison of effectiveness rather than the optimum quantity used. In most cases, the tailings values may be reduced by changing the amount of reagent used. There is a relationship between concentrate grade and tailings grade, which in most metallurgical operations indicates that a double flotation step must be utilized in order to control the grade of one or the other at each particular step, especially where the tails grade is too high. The middlings product of any double flotation step is reground for further processing. The concentrates of the tests ranged in grade from 92 to 97 percent potassium chloride.

The test procedure was substantially the same in each case and was substantially as follows: crushed sylvinite ore was screened to provide a material in the size range of minus 6 to plus 28 mesh. The screened cm was slurried in a saturated brine of the soluble constituents of the ore, and the slurry was then drained to remove any fine material and excess liquid. The amine reagent and the modifying reagent were then added to a 50 gram batch of ore and mixed thoroughly with a stirring rod so that the reagent was thoroughly dispersed in the ore for selectively coating the sylvite particles. The conditioned ore was placed in a flotation cell of about 165 milliliter capacity, clear brine was added to the ore, and

a brine-air jet which was directed downwardly toward the bottom of the cell, substantially as described in our co-pending application, Serial No. 526,720, was turned on. The aerated brine from the jet kept the particles in active suspension in the cell, and, also, introduced additional amounts of brine. The aerated sylvite particles rose to the brine surface and the gangue remained in the cell. The overflowing brine carried the floating sylvite particles over a product weir out of the cell. Complete flotation action was accomplished in about fifteen seconds. The flotation was accomplished with substantially no froth forming on the surface of the brine, and the air bubbles reaching the brine surface broke almost as soon as they contacted the atmosphere.

The following table shows a summary of tests using reagents according to the invention. Except as otherwise designated, an ore of minus 6 to plus 28 mesh ore is used.

Hydro Modifier, genated 'failing, Modifier Lb./ton Tallow Percent Amine, K01 Lb./ton

Aliphatic Alcohols:

Dimethyl hexanols. 2. 68 0.28 8.2 Z-Ethyl-hexyl alcohol 1. 0.28 12.0 4-Methyl pentanol- 2. 97 0.28 12.0 nDecyl alcohol 2.09 D. 28 13. 2 2-Ethyl-isohexyl alcohol 1. 66 0.28 14. 6 Alicyclic Alcohols:

Hydroabietyl alcohol in Kero- 0.28 0 19 3 3 sene solution 1. 32 Para-menthane alcohol 3. 97 0.28 8 6 Pinane alcohol 1.37 0.28 r 4 Esters of Cyclic Acids:

Methyl ester of abietic aeid 3. 50 0. 20 12. a 15% Methyl esters of abietie acid, Methanol 1.52 0.28 3 6 Methyl esters of tall oil (-8 mesh ore) 0. 77 0.26 0 7 Esters of Fatty Acids:

Methyl esters of tallow 1.12 0. l6 5 6 50% Methyl esters of hydrogehated tallow 50% 4-Methyl pentanol-Z 8 mesh ore 0.87 0.10 0. 0 7 Methyl esters of fish oil (-8 so ltfti rt ai" ii iii 6 0 e y es ers o 1 50% Dimcthyl hexanols o. 51 i a 50% Methyl esters of tallow, 0.49 0 12 4 0 50% Kerosene 0.49 Glycerol Esters of Fatty Acids:

Crude cottonseed oil 1. 23 0.12 2.7 Distilled cottonseed oil. 2. 39 0. 28 2. 3 Linseed oil 2. 68 0.28 6. 5 Hydrogenated cottonseed 1. 16 g 1. 6 v u.

10% Methylene bis-stearamide, 0.30

Dirnethylhcxanols 2.70 0 16 3 0 20% Amide of hydrogenated tallow acids in 80% Dlmethyl 0.67 0. 28 5 5 N hexanols 2. 68

one:

Normal reagent rate for amine... 0. 0 0. 28 0) High reagent rate for amine 0.0 1. 08

1 No flotation. 2 Only a trace floated.

The rates of reagent used, as noted in the table, vary considerably. The rate of amine reagent may be very low, and in some cases actually substantially less than the amount required in the froth flotatio'n of standard sizes of ore. As used herein, the amine only furnishes attachment between the modifier and the main flotation particles. To a considerable extent the rate of modifier required may be dependent on the efiiciency of its distribution in the ore. Some of the modifiers require considerable quantities when used alone, while very small quantities may be eflective if the reagent has been placed ously referred to and in which these reagents are to be used, is so effective that small quantities of reagents and new reagents not before reported are effective in the flo'tation separation. The small amount of amine reagent and the small amount of modifier produces a reagent which is highly selective and etficient, and it provides unexpectedly strong floating characteristics for the large sizes of potash mineral. As flotation is rapid, flo'tation cell capacity is high.

While the invention has been illustrated by reference to specific embodiments, there is no intent to limit the concept and the scope of the invention to the precise details so described, except insofar as set forth in the following claims.

We claim:

1. In the ore dressing art in which sylvite is concentrated from coarse sylvinite ores crushed and sized to about 6 to +28 mesh range, deslimed and then suspended in an aqueous solution of at least one of the soluble constituents of the ore, the improvement which comprises conditioning a pulp of the ore with small and eifective amounts of an aliphatic amine to selectively coat substantially all of the sylvite constituent, and then adding to the amine coating on the conditioned ore a non-polar highly hydrophobic modifier consisting of high molecular weight alcohols, said modifiers being miscible with said amine collector and not selectively attracted to the potassium constituent whereby to produce a coating on the sylvite constituent which is substantially more hydrophobic than an amine coating, conditioning said mixture and then subjecting said conditioned ore to a frothless flotation in which a slurry of the conditioned ore is aerated to produce an upward movement of the particles suspended therein and in which the selectively coated sylvite will float on the surface of the brine in the absence of a froth bed.

2. A concentration treatment according to claim 1 in which the high molecular weight alcohols are aliphatic mono-hydric alcohols.

3. A concentration treatment according to claim 1 in which the high molecular weight alcohols are alicyclic mono-hydric alcohols.

4. In the ore dressing art in which sylvite is concentrated from coarse sylvinite ores crushed and sized to about -6 to +28 mesh range, deslimed and then suspended in an aqueous solution of at least o'ne of the soluble constituents of the ore, the improvement which comprises conditioning a pulp of the ore with small and effective amounts of an aliphatic amine to selectively co'at substantially all of the sylvite constituent, and then adding to the amine coating on the conditioned ore a non-polar highly hydrophobic modifier consisting of esters of high molecular weight organic acids, said modifiers being miscible with said amine collector and not selectively attracted to the potassium constituent whereby to produce a coating on the sylvite constituent whichl is substantially more hydrophobic than an amine coating, conditioning said mixture and then subjecting said conditioned ore to a frothless flotation in which a slurry of the conditioned ore is aerated to produce an upward movement of the particles suspended therein and in which the selectively coated sylvite will float on the surface of the brine in the absence of a froth bed.

5. A concentration treatment according to claim 4 in which the high molecular weight acids are cyclic acids.

6. A concentration treatment according to claim 4 in which the high molecular weight acids are fatty acids.

7. In the ore dressing art in which sylvite is concentrated from coarse sylvinite ores crushed and sized to about 6 to +28 mesh range, deslimed and then suspended in an aqueous solution of at least one of the soluble constituents of the ore, the improvement which comprises conditioning a pulp of the ore with small and effective amounts of an aliphatic amine to selectively coat substantially all of the sylvite constituent, and then adding to the amine coating on the conditioned ore a non-polar highly hydrophobic modifier consisting of amides of high molecular weight fatty acids, said modifiers being miscible with said amine collector and not selectively attracted to the potassium constituent whereby to produce a coating on the sylvite constituent which is substantially more hydrophobic than an amine coating, conditioning said mixture and then subjecting said conditioned ore to a frothless flotation in which a slurry of the conditioned ore is aerated to produce an upward movement of the particles suspended therein and in which the selectively coated sylvite will float on the surface of the brine in the absence of a froth bed.

8. A concentration treatment according to claim 7 in which a mixture of at least two modifiers are utilized to modify the aliphatic amine coating on the sylvite particles.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Taggart: Handbook of Mineral Dressing, 1945, Sec. 12, pages 17-18.

Taggart: Handbook of Mineral Dressing, 1945, Wiley, pages 12-50, 12-51, 1252. 

1. IN THE ORE DRESSING ART IN WHICH SYLVITE IS CONCENTRATED FROM COARSE SYLVINITE ORES CRUSHED AND SIZED TO ABOUT -6 TO +28 MESH RANGE, DESLIMED AND THEN SUSPENDED IN AN AQUEOUS SOLUTION OF AT LEAST ONE OF THE SOLUBLE CONSTITUENTS OF THE ORE, THE IMPROVEMENT WHICH COMPRISES CONDITIONING A PULP OF THE ORE WITH SMALL AND EFFECTIVE AMOUNTS OF AN ALIPHATIC AMINE TO SELECTIVELY COAT SUBSTANTIALLY ALL OF THE SYLVITE CONSTITUENT, AND THEN ADDING TO THE AMINE COATING ON THE CONDITIONED ORE A NON-POLAR HIGHLY HYDROPHOBIC MODIFIER CONSISTING OF HIGH MOLECULAR WEIGHT ALCOHOLS, SAID MODIFIERS BEING MISCIBLE WITH SAID AMINE COLLECTOR AND NOT SELECTIVELY ATTRACTED TO THE POTASSIUM CONSTITUENT WHEREBY TO PRODUCE A COATING ON THE SYLVITE CONSTITUENT WHICH IS SUBSTANTIALLY MORE HYDROPHOBIC THAN AN AMINE COATING, CONDITIONING SAID MIXTURE AND THEN SUBJECTING SAID CONDITIONED ORE TO A FROTHLESS FLOTATION IN WHICH A SLURRY OF THE CONDITIONED ORE IS AERATED TO PRODUCE AN UPWARD MOVEMENT OF THE PARTICLES SUSPENDED THEREIN AND IN WHICH THE SELECTIVELY COATED SYLVITE WILL FLOAT ON THE SURFACE OF THE BRINE IN THE ABSENCE OF A FROTH BED. 